In the manufacture of glass articles it is standard to feed molten glass to a plurality of nozzles that continuously emit respective strands of molten glass. Cutters sever gobs (also referred to as slugs) from the emerging strand and these gobs are then fed to respective preform holders where they are conditioned, that is heated or cooled to a predetermined temperature, before being actually molded or otherwise transformed into the desired finished shape.
The cutting device has a plurality of pairs of cutting blades whose cutting edges are movable from a starting position, in which the glass strand flows between the respective cutting blades, into a working position in which each glass strand is severed with the formation of a gob, and back into the starting position. The gobs are deposited into a preform having multiple adjacently spaced blank molds where the separated gobs are optionally shaped into blanks. A shaping device can receive the blanks from the preform and processing them into glass articles. The travel paths through which the gobs move from the severing and separation stage to the preform molds have different lengths.
Normally the strands are extruded vertically downward, that is in the vertical direction, and the cutter blades are movable horizontally, that is in the horizontal direction. The travel paths through which the freshly formed gobs path can extend in both the X and vertical directions, and are invariably of different lengths.
U.S. Pat. No. 6,289,696 of Bogert describes a device where a pair of arms pivotal about respective vertical axes each carry a plurality of blades. The arms can be pivoted together, scissor-like, to substantially simultaneously sever a respective gob from a strand oriented between a pair of blades. The blades of each arm are fixed relative to each other and, hence, move synchronously. Thus the gobs are formed substantially simultaneously and therefore, on their way to the respective preform molds, travel different distances and, as a result, cool differently by the time they reach the preform mold.
EO 0,712,812 of Giraudo has a system where the cutting blades of a cutting blade pair may be moved linearly and horizontally. Here as well, multiple glass strands flow vertically in the vertical direction between the open cutting blade pair, and are severed by the horizontal linear movement of the cutting blades. Each of the left and right cutting blades is mounted on a separate carrier. Each carrier may be actuated by means of a linear electric motor, thus enabling all the cutting blades to move together into the separating position and into the starting position.
In both of these known devices, when the cutting blades are moved into the closed position the glass strand accumulates atop the cutting blades and is compressed. This disturbs the droplet fall, causing the gobs separated from the glass strand to be deformed. This effect is disadvantageous for the subsequent processing of the gob. For this reason it is known to provide an auxiliary device as shown in FIG. 2 having a supply 1′ into which molten glass flows via a rotary tube 2′. The level of the glass melt is indicated by reference numeral 3′. A strand 4′ of molten glass flows downward in direction Z from the supply 1′. The glass strand 4′ is severed by means of a pair of cutting blades 5′ and 6′, and a gob 7′ is separated and delivered to an unillustrated preform. To prevent the glass strand 4′ from accumulating on the cutting blades 5′ and 6′ during the separation procedure for the gob 7′, a plunger 8′ is provided which may be moved in the direction of the arrow 9′. During the cutting operation this plunger 8′ is moved back, i.e., moved upward in the direction of the arrow 9′, in order to move the glass strand 4′ back during the cutting operation, thus preventing the glass strand from accumulating on the cutting blades 5′, 6′ and being deformed. Such a system is complicated. For a high cutting frequency of the cutting blade pairs it is less efficient. The cutting frequency may be 200 cuts per minute, for example.
Another disadvantageous effect occurs when multiple gobs 7′ from a plurality of glass strands 4′ are simultaneously separated and are delivered to adjacently positioned preforms 10′. This procedure is illustrated in FIG. 5. The gob 7′ on the right is the first to arrive at the preform 10′ at station C, and due to the different distances from the cut point to the preform 10′ the second gob 7′ requires a longer time to arrive at the preform 10′ at station B. Finally, the left gob 7′ in FIG. 5 requires the longest time to arrive at the preform 10′ at station A. As a result, the gob 7′ in preform station C has a longer residence time than the gob 7′ for preform station A. The preforming work step cannot begin until all gobs 7′ have arrived at the corresponding preforms 10′. Due to the longer residence time, the gob 7′ for preform 10′ in station C is situated lower on the muzzle tool for preform station C, which also results in greater heating in the region of preform 10′ of station C. On the other hand, the temperature of the gob 7′ in preform 10′ at station C is less than in the region of preform 10′ at station A. This means that problematic differing cooling adjustments must be taken into account.